Colloidal Quantum-Dot Photodetectors Exploiting Multiexciton Generation
Vlad Sukhovatkin,
Sean Hinds,
Lukasz Brzozowski,
Edward H. Sargent*
Multiexciton generation (MEG) has been indirectly observed in
colloidal quantum dots, both in solution and the solid state,
but has not yet been shown to enhance photocurrent in an optoelectronic
device. Here, we report a class of solution-processed photoconductive
detectors, sensitive in the ultraviolet, visible, and the infrared,
in which the internal gain is dramatically enhanced for photon
energies
Ephoton greater than 2.7 times the quantum-confined
bandgap
Ebandgap. Three thin-film devices with different quantum-confined
bandgaps (set by the size of their constituent lead sulfide
nanoparticles) show enhancement determined by the bandgap-normalized
photon energy,
Ephoton/
Ebandgap, which is a clear signature
of MEG. The findings point to a valuable role for MEG in enhancing
the photocurrent in a solid-state optoelectronic device. We
compare the conditions on carrier excitation, recombination,
and transport for photoconductive versus photovoltaic devices
to benefit from MEG.
* To whom correspondence should be addressed. E-mail: ted.sargent{at}utoronto.ca
